US20010004372A1 - Arrangement and method for measuring the temperature of a fluid - Google Patents
Arrangement and method for measuring the temperature of a fluid Download PDFInfo
- Publication number
- US20010004372A1 US20010004372A1 US09/733,044 US73304400A US2001004372A1 US 20010004372 A1 US20010004372 A1 US 20010004372A1 US 73304400 A US73304400 A US 73304400A US 2001004372 A1 US2001004372 A1 US 2001004372A1
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- US
- United States
- Prior art keywords
- measuring
- current
- measuring sensor
- measurement
- voltage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K13/00—Thermometers specially adapted for specific purposes
- G01K13/02—Thermometers specially adapted for specific purposes for measuring temperature of moving fluids or granular materials capable of flow
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
- G01F1/696—Circuits therefor, e.g. constant-current flow meters
- G01F1/698—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
- G01F1/6986—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters with pulsed heating, e.g. dynamic methods
Definitions
- the invention relates to an arrangement and a method for measuring the temperature of a fluid with a measuring sensor to which a measuring current is applied by a current source.
- An arrangement for the combined measurement of the flow velocity and the temperature of a gas is known, for example, from U.S. Pat. No. 3,645,133.
- a hot wire in a gas channel is heated to an operating temperature and this hot wire is connected to a measuring bridge.
- a measurement value proportional to the flow velocity results from a bridge unbalance.
- a measuring sensor is present through which the flow likewise flows and influences the current supply unit of the measuring bridge.
- a constant overtemperature adjusts at the hot wire compared to the gas temperature because of the compensation of the temperature influence.
- the known arrangement is preferred for use in ventilating systems in order to measure the gas volume which is inhaled or exhaled by the patient or even to measure the minute volume.
- the current which flows through the measuring sensor, leads however to an inherent warming so that it is not the actual gas temperature which is determined but a measurement value which, in a complex manner, includes the inherent warming of the measurement sensor and the instantaneous flow velocity of the gas in addition to the gas temperature. If one proceeds from a usually flowing measurement current of approximately 10 to 15 milliamperes, then a reduction of the current would considerably reduce the inherent warming but then, simultaneously, the measuring voltage would also drop greatly and the measuring voltage would change only in the order of magnitude of approximately 20 microvolts per degree Kelvin. The further processing of such small measurement voltages requires a very high complexity of circuitry especially when longer feed lines and contact connections between the measuring sensors and the evaluation unit are necessary.
- the arrangement of the invention is for measuring the temperature of a fluid and includes: a measuring sensor disposed in the fluid and having an ohmic resistance; a current source for generating and supplying measuring current pulses to the measuring sensor; a voltage detector connected to the measuring sensor for detecting a measurement voltage (U M ) across the measuring sensor; a current detector for detecting the measurement current (I M ) corresponding to the measurement voltage (U M ); a switching circuit for forming a quotient from the measurement voltage (U M ) and the measurement current (I M ) with the quotient (U M /I M ) indicating the ohmic resistance of the measuring sensor.
- the method of the invention is for measuring the temperature of a fluid and includes the steps of: providing a measuring sensor disposed in the fluid and the measuring sensor having an ohmic resistance; applying measuring current pulses to the measuring sensor thereby causing a measurement voltage (U M ) to drop across the measuring sensor; detecting the measurement voltage (U M ) and the measurement current (I M ) corresponding thereto; and, forming a quotient (U M /I M ) from the measurement voltage (U M ) and the measurement current (I M ) which indicates the ohmic resistance of the measuring sensor.
- the advantage of the invention is essentially that the power, which is supplied to the measuring sensor, can be greatly reduced by selecting a short switch-on time of the measuring current without having to reduce the amplitude of the measuring current.
- a switch-on time of, for example, 50 microseconds within a period duration of 5 milliseconds effects a reduction of the supplied power by a value of approximately 1:100.
- the evaluation can be carried out with measuring currents and measuring voltages which can be processed with a switching complexity which is not excessive without this leading to a significant inherent warming of the measuring sensor.
- the measuring method comprises applying measuring current pulses to the measuring sensor; detecting the measuring voltage U M which drops across the measuring sensor and is generated by the measuring current pulses, and detecting the corresponding measuring current I M ; and, forming the quotient of the measuring voltage U M and the measuring current I M .
- the quotient provides the ohmic resistance of the measuring sensor and is an index for the temperature of the fluid. It has been shown advantageous to take off the measuring voltage and measuring current synchronously at the end of the measuring current pulse when the transient action is completed.
- the voltage maximum U M can be determined with a peak voltage detector and, as a measuring current, the measuring current maximum I M can be detected with a peak current detector.
- FIG. 1 is a schematic of a measuring arrangement according to the invention
- FIG. 2 a shows the time-dependent trace of the control pulse U s (t) of the pulse voltage source of the measuring arrangement of FIG. 1;
- FIG. 2 b is a time-dependent trace of the current I(t) at the measuring sensor
- FIG. 2 c shows the time-dependent trace of the voltage U(t) also at the measuring sensor.
- FIG. 3 is a graph showing the inherent warming of the measuring sensor in dependence upon the square of the measuring current and the ratio of the switch-on time to the period duration.
- FIG. 1 shows schematically a measuring arrangement 1 with which the flow velocity is measured in combination with the gas temperature.
- a hot wire 3 for measuring the flow velocity is mounted in a channel 2 through which the gas flows and a measuring sensor 4 for measuring temperature is also mounted in the channel 2 .
- the hot wire 3 is heated by a control circuit 8 to a constant overtemperature compared to the gas temperature.
- the throughflow direction of the channel 2 is indicated exemplary by an arrow 5 .
- the hot wire 3 and the measuring sensor 4 comprise thin platinum wires which are attached to support wires ( 6 , 7 ) within the channel 2 .
- the control circuit 8 includes a control circuit (not shown in FIG. 1) with which the ohmic resistance of the hot wire 3 is maintained at a pregiven value.
- the hot wire 3 cools down with gas flowing through the channel 2 so that the current flowing through the hot wire 3 is increased by the control circuit 8 .
- the change of the heating current is an index for the flow velocity of the gas.
- the hot wire is controlled by the control circuit 8 to a constant overtemperature relative to the gas temperature. For this reason, the gas temperature must be additionally detected with the measuring sensor 4 .
- the measuring sensor 4 is connected via a series resistor 9 and a switch 10 to a current source 11 .
- the switch 10 comprises three contact arms ( 12 , 13 , 14 ) and is driven with control pulses U s by a pulse voltage source 15 so that the contact arms ( 12 , 13 , 14 ) are closed for short time intervals t e and are thereafter reopened.
- the output signals of the amplifiers ( 16 , 17 ) reach a voltage detector 18 and a current detector 19 via contact arms ( 13 , 14 ), respectively.
- the measuring voltage U M which drops across measuring sensor 4 , and the measuring current I M are determined with detectors ( 18 , 19 ) when the contact arms ( 12 , 13 , 14 ) are closed.
- the detectors ( 18 , 19 ) receive synchronous pulses from an evaluation unit 21 in order to detect the measuring voltage U M and the measuring current I M at the same time point. The time point is so selected that it lies at the end of the control pulse when the transient action is finished.
- Switching circuit 20 is connected downstream of the detectors ( 18 , 19 ).
- the switching circuit 20 is part of the evaluation unit 21 and the quotient of U M and I M is formed in the switching circuit 20 .
- This quotient indicates the ohmic resistance of the measuring sensor 4 and therefore the temperature of the gas.
- the temperature measuring signal is transmitted further via a line 22 to the control circuit 8 so that the gas temperature, which is required for the control to the constant overtemperature, can be considered in the control circuit 8 .
- FIG. 2 a shows, as exemplary, the time-dependent trace of the control pulses U s (t) of the pulse voltage source 15 .
- FIG. 2 b shows the current trace I(t) at the measuring element 4 and
- FIG. 2 c shows the voltage trace U(t) at the measuring element 4 .
- the switch-on time t e amounts, for example, to 50 microseconds for a period duration t p of 5 milliseconds. Within the switch-on time t e , the voltage and current increase to the maximum values U M and I M , respectively. In the present case, the current amplitude is 20 milliamperes.
- the influence of the pulse operation on the inherent warming of the measuring sensor 4 is shown in FIG. 3.
- the inherent warming is plotted along the ordinate as a difference (T-T o ) referred to a reference temperature T o ; whereas, the square of the current I(t), which flows through the measuring sensor 4 , is plotted along the abscissa.
- the ratio (t e /t p ) of the switch-on time t e to the period duration t p is given.
- individual measuring points are connected to form a deviation line. In the ideal case, a linear relationship is present between the inherent warming of the measuring sensor 4 and the square of the measuring current I 2 (t), that is, the supplied power.
Abstract
An arrangement for measuring the temperature of fluids has a measuring sensor (4) to which a measuring current is supplied by a current source (11). This arrangement is improved in that the temperature measurement is carried out without significant inherent warming of the measuring sensor (4). The invention is also directed to a method for carrying out the temperature measurement wherein measuring current pulses are applied to the measuring sensor (4) and the voltage maximum and current maximum, which are generated by the measuring current pulses, drop across the measuring sensor (4) and are detected. A quotient of the voltage maximum and the current maximum is formed and this quotient is an index for the temperature of the fluid.
Description
- The invention relates to an arrangement and a method for measuring the temperature of a fluid with a measuring sensor to which a measuring current is applied by a current source.
- An arrangement for the combined measurement of the flow velocity and the temperature of a gas is known, for example, from U.S. Pat. No. 3,645,133. To measure the flow velocity, a hot wire in a gas channel is heated to an operating temperature and this hot wire is connected to a measuring bridge. A measurement value proportional to the flow velocity results from a bridge unbalance. To compensate for the influence of temperature of the flow velocity measurement, a measuring sensor is present through which the flow likewise flows and influences the current supply unit of the measuring bridge. A constant overtemperature adjusts at the hot wire compared to the gas temperature because of the compensation of the temperature influence. The known arrangement is preferred for use in ventilating systems in order to measure the gas volume which is inhaled or exhaled by the patient or even to measure the minute volume.
- In a temperature measurement, the current, which flows through the measuring sensor, leads however to an inherent warming so that it is not the actual gas temperature which is determined but a measurement value which, in a complex manner, includes the inherent warming of the measurement sensor and the instantaneous flow velocity of the gas in addition to the gas temperature. If one proceeds from a usually flowing measurement current of approximately 10 to 15 milliamperes, then a reduction of the current would considerably reduce the inherent warming but then, simultaneously, the measuring voltage would also drop greatly and the measuring voltage would change only in the order of magnitude of approximately 20 microvolts per degree Kelvin. The further processing of such small measurement voltages requires a very high complexity of circuitry especially when longer feed lines and contact connections between the measuring sensors and the evaluation unit are necessary.
- It is an object of the invention to provide an arrangement and a measuring method to carry out a temperature measurement within a fluid channel without significant inherent warming of the measuring sensor.
- The arrangement of the invention is for measuring the temperature of a fluid and includes: a measuring sensor disposed in the fluid and having an ohmic resistance; a current source for generating and supplying measuring current pulses to the measuring sensor; a voltage detector connected to the measuring sensor for detecting a measurement voltage (UM) across the measuring sensor; a current detector for detecting the measurement current (IM) corresponding to the measurement voltage (UM); a switching circuit for forming a quotient from the measurement voltage (UM) and the measurement current (IM) with the quotient (UM/IM) indicating the ohmic resistance of the measuring sensor.
- The method of the invention is for measuring the temperature of a fluid and includes the steps of: providing a measuring sensor disposed in the fluid and the measuring sensor having an ohmic resistance; applying measuring current pulses to the measuring sensor thereby causing a measurement voltage (UM) to drop across the measuring sensor; detecting the measurement voltage (UM) and the measurement current (IM) corresponding thereto; and, forming a quotient (UM/IM) from the measurement voltage (UM) and the measurement current (IM) which indicates the ohmic resistance of the measuring sensor.
- The advantage of the invention is essentially that the power, which is supplied to the measuring sensor, can be greatly reduced by selecting a short switch-on time of the measuring current without having to reduce the amplitude of the measuring current. A switch-on time of, for example, 50 microseconds within a period duration of 5 milliseconds effects a reduction of the supplied power by a value of approximately 1:100. In this way, the evaluation can be carried out with measuring currents and measuring voltages which can be processed with a switching complexity which is not excessive without this leading to a significant inherent warming of the measuring sensor.
- The measuring method according to the invention comprises applying measuring current pulses to the measuring sensor; detecting the measuring voltage UM which drops across the measuring sensor and is generated by the measuring current pulses, and detecting the corresponding measuring current IM; and, forming the quotient of the measuring voltage UM and the measuring current IM. The quotient provides the ohmic resistance of the measuring sensor and is an index for the temperature of the fluid. It has been shown advantageous to take off the measuring voltage and measuring current synchronously at the end of the measuring current pulse when the transient action is completed. Alternatively, as a voltage, the voltage maximum UM can be determined with a peak voltage detector and, as a measuring current, the measuring current maximum IM can be detected with a peak current detector.
- The invention will now be described with reference to the drawings wherein:
- FIG. 1 is a schematic of a measuring arrangement according to the invention;
- FIG. 2a shows the time-dependent trace of the control pulse Us(t) of the pulse voltage source of the measuring arrangement of FIG. 1;
- FIG. 2b is a time-dependent trace of the current I(t) at the measuring sensor;
- FIG. 2c shows the time-dependent trace of the voltage U(t) also at the measuring sensor; and,
- FIG. 3 is a graph showing the inherent warming of the measuring sensor in dependence upon the square of the measuring current and the ratio of the switch-on time to the period duration.
- FIG. 1 shows schematically a measuring arrangement1 with which the flow velocity is measured in combination with the gas temperature. A
hot wire 3 for measuring the flow velocity is mounted in achannel 2 through which the gas flows and a measuring sensor 4 for measuring temperature is also mounted in thechannel 2. Thehot wire 3 is heated by acontrol circuit 8 to a constant overtemperature compared to the gas temperature. The throughflow direction of thechannel 2 is indicated exemplary by an arrow 5. Thehot wire 3 and the measuring sensor 4 comprise thin platinum wires which are attached to support wires (6, 7) within thechannel 2. Thecontrol circuit 8 includes a control circuit (not shown in FIG. 1) with which the ohmic resistance of thehot wire 3 is maintained at a pregiven value. - The
hot wire 3 cools down with gas flowing through thechannel 2 so that the current flowing through thehot wire 3 is increased by thecontrol circuit 8. The change of the heating current is an index for the flow velocity of the gas. The hot wire is controlled by thecontrol circuit 8 to a constant overtemperature relative to the gas temperature. For this reason, the gas temperature must be additionally detected with the measuring sensor 4. The measuring sensor 4 is connected via aseries resistor 9 and aswitch 10 to acurrent source 11. Theswitch 10 comprises three contact arms (12, 13, 14) and is driven with control pulses Us by apulse voltage source 15 so that the contact arms (12, 13, 14) are closed for short time intervals te and are thereafter reopened. In this way, current and voltage pulses occur at the measuring sensor 4 which are detected with the amplifiers (16, 17). Theamplifier 16 measures the voltage drop across theseries resistor 9 and thereby a quantity proportional to the current; whereas, theamplifier 17 evaluates the voltage drop at measuring sensor 4. - The output signals of the amplifiers (16, 17) reach a
voltage detector 18 and acurrent detector 19 via contact arms (13, 14), respectively. The measuring voltage UM, which drops across measuring sensor 4, and the measuring current IM are determined with detectors (18, 19) when the contact arms (12, 13, 14) are closed. The detectors (18, 19) receive synchronous pulses from anevaluation unit 21 in order to detect the measuring voltage UM and the measuring current IM at the same time point. The time point is so selected that it lies at the end of the control pulse when the transient action is finished. -
Switching circuit 20 is connected downstream of the detectors (18, 19). Theswitching circuit 20 is part of theevaluation unit 21 and the quotient of UM and IM is formed in theswitching circuit 20. This quotient indicates the ohmic resistance of the measuring sensor 4 and therefore the temperature of the gas. The temperature measuring signal is transmitted further via aline 22 to thecontrol circuit 8 so that the gas temperature, which is required for the control to the constant overtemperature, can be considered in thecontrol circuit 8. - FIG. 2a shows, as exemplary, the time-dependent trace of the control pulses Us(t) of the
pulse voltage source 15. FIG. 2b shows the current trace I(t) at the measuring element 4 and FIG. 2c shows the voltage trace U(t) at the measuring element 4. The switch-on time te amounts, for example, to 50 microseconds for a period duration tp of 5 milliseconds. Within the switch-on time te, the voltage and current increase to the maximum values UM and IM, respectively. In the present case, the current amplitude is 20 milliamperes. The influence of the pulse operation on the inherent warming of the measuring sensor 4 is shown in FIG. 3. The inherent warming is plotted along the ordinate as a difference (T-To) referred to a reference temperature To; whereas, the square of the current I(t), which flows through the measuring sensor 4, is plotted along the abscissa. The ratio (te/tp) of the switch-on time te to the period duration tp is given. In FIG. 3, individual measuring points are connected to form a deviation line. In the ideal case, a linear relationship is present between the inherent warming of the measuring sensor 4 and the square of the measuring current I2 (t), that is, the supplied power. - The effects of the current-pulse operation on the inherent warming will now be presented with respect to two numerical examples.
- A measuring current I(t) of 20 milliamperes flows continuously through the measuring sensor4 with te/tp equal 1 leads to an inherent warming of approximately 9.8°C. (parameter A). By clocking the measuring current with a ratio te/tp equal to 1:10, the inherent warming reduces for the same current amplitude to 1.5° C. (parameter B). From FIG. 3, suitable currents I(t) and clock ratios te/tp can be taken at a given inherent warming (T-To).
- It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (5)
1. An arrangement for measuring the temperature of a fluid, the arrangement comprising:
a measuring sensor disposed in said fluid and having an ohmic resistance;
a current source for generating and supplying measuring current pulses to said measuring sensor;
a voltage detector connected to said measuring sensor for detecting a measurement voltage (UM) across said measuring sensor;
a current detector for detecting the measurement current (IM) corresponding to said measurement voltage (UM);
a switching circuit for forming a quotient from said measurement voltage (UM) and said measurement current (IM) with said quotient (UM/IM) indicating said ohmic resistance of said measuring sensor.
2. A method for measuring the temperature of a fluid, the method comprising the steps of:
providing a measuring sensor disposed in said fluid and said measuring sensor having an ohmic resistance;
applying measuring current pulses to said measuring sensor thereby causing a measurement voltage (UM) to drop across said measuring sensor;
detecting said measurement voltage (UM) and the measurement current (IM) corresponding thereto; and,
forming a quotient (UM/IM) from said measurement voltage (UM) and said measurement current (IM) which indicates said ohmic resistance of said measuring sensor.
3. The method of , wherein the maximum values of said measurement voltage (UM) and said measurement current (IM) are taken to form said quotient.
claim 2
4. The method of , comprising the further step of adjusting the amplitude of said measurement current to values lying in the range of 5 to 20 milliamperes.
claim 3
5. The method of , comprising the further step of adjusting the ratio of the pulse duration te to the period duration tp of said measurement current to values lying in a range of 1:10 to 1:100.
claim 3
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE19960429.0 | 1999-12-15 | ||
DE19960429A DE19960429A1 (en) | 1999-12-15 | 1999-12-15 | Device and method for measuring the temperature of a fluid |
Publications (1)
Publication Number | Publication Date |
---|---|
US20010004372A1 true US20010004372A1 (en) | 2001-06-21 |
Family
ID=7932719
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/733,044 Abandoned US20010004372A1 (en) | 1999-12-15 | 2000-12-11 | Arrangement and method for measuring the temperature of a fluid |
Country Status (3)
Country | Link |
---|---|
US (1) | US20010004372A1 (en) |
DE (1) | DE19960429A1 (en) |
FR (1) | FR2802635A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1441206A1 (en) * | 2003-01-16 | 2004-07-28 | Dwyer Instruments, Inc. | Sensor temperature control in a thermal anemometer |
US20060096305A1 (en) * | 2004-11-11 | 2006-05-11 | Keiji Hanzawa | Fluid flowmeter and engine control system using the same |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE102014204604B4 (en) * | 2014-03-12 | 2021-05-06 | BSH Hausgeräte GmbH | Household appliance with a volume flow sensor in a pipe for a fluid |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3645133A (en) * | 1970-04-15 | 1972-02-29 | Metrophysics Inc | Electronic spirometer |
CA1255923A (en) * | 1985-12-23 | 1989-06-20 | Dimitri Petrov | Non-obstructive thermodynamic flow meter |
US5685194A (en) * | 1995-07-27 | 1997-11-11 | Delta M Corporation | Differential twin sensor system |
JPH09218065A (en) * | 1996-02-13 | 1997-08-19 | Murata Mfg Co Ltd | Thermal flowrate sensor |
-
1999
- 1999-12-15 DE DE19960429A patent/DE19960429A1/en not_active Withdrawn
-
2000
- 2000-12-05 FR FR0015761A patent/FR2802635A1/en active Pending
- 2000-12-11 US US09/733,044 patent/US20010004372A1/en not_active Abandoned
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1441206A1 (en) * | 2003-01-16 | 2004-07-28 | Dwyer Instruments, Inc. | Sensor temperature control in a thermal anemometer |
US20040199354A1 (en) * | 2003-01-16 | 2004-10-07 | Heuer Daniel A. | Sensor temperature control in a thermal anemometer |
US6905242B2 (en) | 2003-01-16 | 2005-06-14 | Dwyer Instruments, Inc. | Sensor temperature control in a thermal anemometer |
US20060096305A1 (en) * | 2004-11-11 | 2006-05-11 | Keiji Hanzawa | Fluid flowmeter and engine control system using the same |
Also Published As
Publication number | Publication date |
---|---|
DE19960429A1 (en) | 2001-07-05 |
FR2802635A1 (en) | 2001-06-22 |
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AS | Assignment |
Owner name: DRAEGER MEDIZINTECHNIK GMBH, GERMANY Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ENGEL, DIETER;REEL/FRAME:011455/0956 Effective date: 20001208 |
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STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |